Well if you're talking about games, It doesn't really matter to me, as long as the game is fun and has a good story, i don't care what dimension it's in.
Ah, ok.
I like movies that use 3D, if it makes it better. (Avatar) If it's used to just be gimmick, (Shark Boy and Lava Girl) it's annoying.
As for games, there's two different ways to think about 3D. If you mean 2D as in sprite animations and retro stuff, and 3D as in most modern games, I prefer 3D. It depends on the game though.
If you're talking about 3D glasses or monitors that refract the pixels to give the illusion of 3D, then I don't know. I've never tried it.